A soldering apparatus is known in the art as the heat-bonding apparatus, having a heating means, in which a heating plate is provided in an openable chamber filled with reducing carboxylic acid vapor (see Patent Document 1, for example). Part of the heating plate on which a substrate is placed is flattened, and a temperature sensor is provided in the heating plate for sensing the temperature of the heating plate. The heating means is configured to control the temperature of the heating plate according to the sensed temperature of the heating plate.